1. Field of the Invention
The present invention relates to a method for controlling a test for an exchange and, more particularly, to a method for controlling a test for an exchange in which a folding test is performed within the exchange.
Recently, various requirements are raised for high speed data communication systems such as a LAN interconnection system, a large capacity file transmission system or a high-speed and highly accurate facsimile transmission system. Also, various requirements have been raised for audio and video communication systems such as a video conference system, a video telephone or a cable television system. Additionally, a multimedia communication which is a combination of data, audio information and video information has become popular, and a demand for a broad band ISDN exchange (ATM exchange) which can be applied to various types of those communication systems has increased. Accordingly, a need has increased to maintain normality of such an asynchronous transfer mode (ATM) exchange by a periodic test.
2. Description of the Related Art
In ATM system in which various kinds of data, audio signals and video signals are transmitted, a cell comprising an information field having 48 bytes and a header having 5 bytes is used. An exchange for switching such cells comprises a central processing device for controlling each section and a line control device which includes a line processing section and a switching section. A subscriber cell is transmitted through the exchange along a route which corresponds to a virtual path identifier (VPI) and a virtual channel identifier (VCI) provided in the header of the cell formed in the line processing section and switching section.
In order to check normality of an exchange, a test cell is transmitted through the exchange so as to determine whether or not the test cell normally transmits the exchange. In this method, a test cell generating device should be provided so as to generate the test cell. The test cell generating device is activated by the central processing device. The test cell generated by the test cell generating device is folded at a designated fold point so as to detect whether or not the test cell normally passed through a designated route. A result of the detection is announced to the central processing device. When the test cell normally passes the designated route, it is determined that the designated route is normal. The determination is performed by detecting a cell loss, a cell error and a bit error.
The above-mentioned test must be periodically performed for all routes within the exchange. In this case, a number of routes to be checked within the exchange is an extremely large number. For example, since the switching section has a multi-stage structure and a large number of intersections are present in each stage, the number of routes passing the intersections is increased as the number of stages is increased. Accordingly, it takes a relatively long time to check all routes by such a test in which a test cell is transmitted and folded.
In order to reduce the test time, a testing method has been suggested in which a plurality of routes are concurrently checked. In this testing method, a folding point is designated for a plurality of routes. Then, a plurality of test cell generating devices are activated so as to generate cells for each of the plurality of routes. The test cells are folded at the respective folding points and detected at substantially the same time.
The central processing device of the exchange controls a call connection and disconnection by controlling the line control device. Additionally, the central processing device controls the periodic test for all routes by activating a plurality of test cell generating devices. Accordingly, there are the following problems.
1) When a periodic test is performed by activating a plurality of test cell generating devices while a large load is applied to the central processing device due to origination of many call connections and disconnections, the load to the central processing device is further increased which results in a high possibility of occurrence of congestion.
2) A fixed load is continuously applied to the central processing device during the periodic test. Thus, when many call connections and disconnections are generated, the load applied to the central processing device is increased which may result in an occurrence of congestion.
3) When a periodic test is performed by activating a plurality of test cell generating devices while a large load is applied to the central processing device for a long time due to origination of many call connections and disconnections, the load to the central processing device is further increased which results in an occurrence of congestion. As a result, the periodic test cannot be completed by a programed time and, thereby, the periodic test may be canceled. Thus, it is possible that a periodic test is not performed for an important route and, thus, normality cannot be assured.